Steel-wire reinforced belts of vulcanized material, e.g. rubber compositions, are fabricated for a variety of purposes. They may, for example, be used as flat drive belts for machinery or for like force-transmission purposes but more generally are employed as conveyor belts for transporting of goods, people or materials over long or short distances within fabrication, chemical, metallurgical or other industrial plants or to and from such plants or elsewhere.
Regardless of the application, it is important that the belts be of high quality, i.e. the bond between the vulcanizable elastomeric material and the steel reinforcing wires have a long life under a wide variety of stress conditions.
Failure of the belts prematurely may result at least in part from relative movement of the reinforcing wires and the surrounding vulcanized material. It has also been found that isotropism is important in such belts, i.e. that the belts have properties which are as uniform as possible over the belt length. Investigations have shown that such isotropism or uniformity of properties over the length of the belt requires uniform wire tension which is reproducibly generated in successive lengths of the belt as it is produced.
In general the apparatus utilized to produce such a belt operates incrementally in units of lengths determined by the length of the vulcanization press.
An apparatus for fabricating such belts thus may have a supply of reinforcing wire, generally in the form of a frame provided with a multiplicity of reels from which the steel wire is paid out and guided through the press.
The wires, generally disposed parallel to one another in at least one plane, thus form a reinforcing layer which can be covered from above and below at a layer-application station with one or more layers of vulcanizable material, the resulting composite thereupon passing into the press in which this material is compacted around the wires and is vulcanized to form a unitary structure to which the wires are bonded and in which they are embedded.
The belt emerging from the opposite end of the press can be wound up on a take-up coil.
Since the composite structure may be stationary during the pressing operation if the press is not movable, it is advantageous to make the layer-application means movable. Thus, when a given unit of length of the belt previously produced in the press is moved outwardly therefrom, the layer-applying device on a movable carriage, may accompany the strands as they shift in the direction of the press so that while the press is closed on the next implement of length and the strands and belt are stationary, the layer-applying device can be shifted in the opposite direction to form another length of the composite adapted to be drawn in the press in the next cycle.
In a specific apparatus for this purpose described in Pressen und Anlagen fur die Gummi-Industrie (Presses and Installations for the Rubber Industry), a brochure published by G. Siempelkamp GmbH & Co., Krefeld, Germany, pages 5 through 7, downstream of the reel frame and a coil storage and upstream of the layer-applying carriage, there is provided a wire clamp which can seize the wires of the reinforcing array, once these wires have been advanced to allow the desired degree of longitudinal prestress to be applied to these wires. The wire clamp thus may have a dual function of seizing the wires to prevent extraction of additional lengths of wire from the reel and of generating in the wire stretch between the clamp and the take-off cord, the desired length degree of longitudinal prestress.
This clamp and stressing device is followed by the layer-applying station which can be movable in the manner described while both the clamping and wire supply devices are flexibly located with respect to the press which can be fixed along the path of the belt as well. The vulcanizing press follows the layer-applying carriage and downstream of the press there is provided a traction clamping device capable of driving the belt through the press and hence the wire reinforcing strands from the respective reel and through the press through the clamping and stressing device and along the path previously described. This tractive clamping means may include separate means for entrainment of the belt and for clamping the latter or a single means performing both directions. The clamping effect is necessary to prevent reverse movement of the belt under traction stresses applied by the wire tensioning means.
Downstream of the tractive clamping means is the take-up coil.
Experience with such apparatus has shown that advance of the previously formed length of belt from the press and extraction of corresponding lengths of wire from the wire supply requires a wire storage as described in the latter publication to ensure that the wire clamp can remain closed during the advance previously mentioned. Unavoidably because of tolerance differences or the like one or more of the wires along the path tends to hang down in a loop from the plane of the array of wires and to introduce nonuniformities in tensioning during the fabrication of the belt.
This slack, if permitted to remain, results in belts of poor quality and, if taken up by hand, results in time-consuming operations which increase the cost of the belt without always guaranteeing that successive length thereof will be of uniformly high quality.
In German patent document DE-OS No. 15 79 088, for example, this wire storage means is eliminated and the wire clamp is located directly ahead of the wire supply device. This does not eliminate the problem, however, since both clamps on opposite sides of the press generally operate by engaging all of the wires simultaneously and uniformly so that any tolerance differences between individual wires may result in a slack.